1. Field of the Invention
The present invention relates to a method of forming bump electrodes on electrode terminals of an electronic component such as a semiconductor element, a passive element, and an electronic circuit module for electrically connecting the electrode terminals with a conductive pattern formed on a wiring board, and an electronic circuit device which is manufactured by utilizing this bump electrode forming method, and which comprises a printed wiring board having an electronic circuit module mounted thereon.
2. Description of the Related Art
In the field of semiconductor integrated circuits, a semiconductor element having more than 100 terminals has been developed as a result of improvements achieved in the field of integration density of semiconductor elements. As a result of the trend toward greater integration density, demand has grown for the development of a technique for efficiently bonding such high-density integrated circuits to a conductive pattern of a wiring board.
In response to this demand, a number of techniques have been developed whereby a large number of electrode terminals of a semiconductor element are collectively bonded to a conductive pattern formed on a wiring board. One such technique is the flip-tip technique, according to which a plurality of electrode terminals are formed on a surface of a semiconductor element, the electrode terminal formation surface of the semiconductor element is placed to face a bonding conductive pattern of a wiring board, and the electrode terminals and the conductive pattern are connected to each other through bump electrodes. Using the flip-tip technique bump electrodes can be formed by way of either one of the two following methods:
According to the first method, a laminated film of Cr/Cu/Au or Ti/Ni/Au is formed on electrode terminals of a semiconductor element by vacuum evaporation and PEP (photo etching process), and then a Pb-Sn alloy solder layer is formed on this laminated film by plating. According to the second method, a Pb-Sn alloy solder layer is formed on connection terminals of a conductive pattern on a wiring board by printing or plating.
These methods, however, require complex processes and high manufacturing costs, and moreover, many defective products tend to be manufactured, especially in the case of the first method, since PEP is required for each wafer. In addition, since each of these methods a entails the formation of a solder layer, by plating or printing, it is difficult to obtain a uniform thickness of this layer, and hence the heights of bump electrodes become nonuniform.
Recently, with a demand for a higher integration density of electronic equipment, an electronic circuit module incorporating semiconductor elements and passive elements such as chip capacitors is used. As a method of manufacturing such an electronic circuit module, a method shown in FIGS. 1A to 1C is known ("Planar LSI interconnection method utilizing polymeric conductor" IMC. Proc. 1986).
In this method, for example, semiconductor elements 1 and 2, and passive element 3 such as a chip capacitor are face-die-mounted onto determined positions within frame body 4 mounted on base member 6 (FIG. 1A). Then, liquid resin 5 is charged into spaces between elements 1 to 3 and frame body 4, and is cured (FIG. 1B). Subsequently, frame body 4 and elements 1 to 3 are separated from base member 6, and a conductive paste such as Ag paste is screen-printed on these elements to simultaneously form wiring for connecting electrodes 7 to the respective elements (FIG. 1C). In this method, since wiring is formed on the surfaces of the elements after the elements are buried in the resin, a thin-profile electronic circuit module can be obtained. In addition, multilayer wiring can be formed, and high-density mounting can be performed, thereby obtaining an extremely compact electronic circuit module.
When a large electronic circuit apparatus is formed by a plurality of such electronic circuit modules or a combination of these modules and other electronic circuit modules, the electronic circuit modules are mounted on a printed board. In this case, a method of connecting the electrode terminals of the electronic circuit modules to the electrodes on the printed board using an anisotropic conductive adhesive sheet obtained by dispersing a solder powder or Ni powder in an organic polymer can be employed.
In such a method, however, since the solder powder or the Ni powder is dispersed in the anisotropic conductive adhesive sheet at random, in order to reliably connect the electrode terminals of the electronic circuit modules to the electrodes of the printed board, the electrode terminals and the electrodes must be increased in size. Since a uniform pressure is not applied to each electrode during the adhesive bonding because of the nonuniform particle diameter of the solder powder or the Ni powder, a stable junction resistance cannot be obtained. In the worst case, the electrodes may be destroyed by the bonding pressure. Furthermore, since the solder powder or the Ni powder cannot be heated to its melting point from the viewpoint of the prevention of heat deterioration of the resin in the electronic circuit modules, the conduction between the anisotropic conductive adhesive sheet, continuity between the electrode terminals of the electronic circuit modules and the electrodes of the printed wiring board is maintained simply by contact. Therefore, a junction failure may be caused due to spring back of a binder resin present in the electronic circuit modules and the adhesive sheet.